The interaction of the cancer chemotherapeutic agent cis-diamminedichloroplatinum(II) (cis-DDP) with DNA appears essential to the action of the drug. The efficacy of the drug can be modulated by the capacity of a cell to repair the damaged DNA or to efficiently replicate on damaged templates. However, these systems are not infallible and toxicity and mutagenicity do result. I intend to investigate these phenomena in murine leukemia L1210 cells and in a cis-DDP resistant subline. The involvement of post-replication repair and recombination as mechanisms to bypass lesions in cis-DDP will be assessed. Single stranded DNA of known base sequence will be used to determine sites of inhibition of replication after cis-DDP modification. Mutagenesis in a whole cell system will be investigated, specifically in the adenine phosphoribosyl transferase gene. This will be performed initially in Chinese Hamster Ovary cells and mutants will be selected with 8-azaadenine. Altered restiction nuclease sites or deletions in the mutant gene will be assessed and DNA sequencing gel electrophoresis will be used to determine the exact nature of the mutation. This can provide information on the critical lesion(s) in DNA. These studies will be facilitated by the availability of [3H]-cis-dichloro(ethylenediamine)platinum(II), an analogue that functions identically to cis-DDP. The chemical character of each DNA-reaction product will be compared to the changes observed in DNA replication and mutagenesis. It is proposed that resistance to cis-DDP may be mediated by a gene amplification process and an attempt will be made to isolate the gene and then the gene product(s) involved. The involvement of aberrant replication in the development of resistance will be assessed. In particular this might involve the transient formation of extrachromosomal DNA as a result of inhibited DNA replication. Throughout comparisons will be made with other platinum analogues, particularly trans-DDP, an ineffective chemotherapeutic drug and a diaminocylohexane analogue that is potentially better than the parent compound, and to which the cis-DDP-resistant L1210 cells are sensitive. By these means I hope to determine the mechanism of action and the mecahanism of resistance to platinum analogues and perhaps provide a basis for further drug development.